Maryland Route 27 is a state highway in the U.S. state of Maryland. Known for most of its length as Ridge Road, the highway runs 39.17 miles (63.04 km) from MD 355 in Germantown north to MD 30 in Manchester. MD 27 follows a ridge that separates several watersheds in northern Montgomery County and Carroll County. The highway connects Germantown and Manchester with Damascus in far northern Montgomery County; Westminster, the county seat of Carroll County; and Mount Airy, which lies at the junction of Carroll, Frederick, Howard, and Montgomery counties and where MD 27 intersects Interstate 70 (I-70)/U.S. Route 40.

Maryland Route 355 (MD 355) is a 36.75-mile (59.14 km) north–south road in western central Maryland in the United States. The southern terminus of the route is in Bethesda in Montgomery County, where Wisconsin Avenue meets the county's border with Washington, D.C. The northern terminus is just north of a bridge over Interstate 70 (I-70)/U.S. Route 40 (US 40) in the city of Frederick in Frederick County, where the road continues north as Market Street through Frederick towards MD 26.